You can also find a little about Pir Tama’s rescue of the Dark Elves ingame. We can gather:
Pir Tama, (‘Peer Tah-mah’) was guided by Cabirus. She wielded a dagger, Pir Tama’s Ire, to lead the rebellion of the Disenthralled Elves from their enthrallment to their wizard master, one of the Obsidian sorcerers who had formed their race to be their slaves.
She died young, but lived long enough to teach her people diplomacy and unity with the factions of the Underworld, welcoming their aid. She died “shortly” (though perhaps some years) after their arrival, in the act of sealing the portal through which they had escaped to the Underworld.
At least, that’s the lore I could find, which I’ve written up at http://underwiki.com/wiki/Characters. Whether that is the truth the book tells, we can’t know - our narrator ingame seems rather unreliable, and all characters have their own motivations and faction biases, so any amount of this could be misremembered, delusions, braggadocio, or even outright lies.
http://sotawiki.net/sota/Elf has Elven lore from the point of view of New Britannia, which mentions an “Obsidian Order”, appearing to tie into this lore.